How are you riding? I donāt even have that high of a number with my 8" mtb and i weigh 100kg.
With my 100mm hubs Iām around 7-9 wh/km
On my mtb 17-19wh/km
Probably just my 9" wheels which arenāt fully pumped up for more traction in the snow. Also I ride aggressively. (Using this battery on my MTB at the moment)
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Ah i thought that the 24wh/km are on your thanes
Arcing easily occurs all the time with āmechanicalā vaping devices using just a single cell. The button on the device presses a contact up against the cell and a spring separates them when the button is released. Each time that is done an arc mark is created.
Some designs can minimize the size of the mark but itās always there.
The arcs are created by the inductance of the system, creating a higher (sometime much higher) voltage to try to keep the current flowing as the contacts separate. You can create large arcs with very low voltages if the inductance is high enough.
When two contacts separate the arc can start when they are a just a tiny distance apart, a millionth of a millimeter or whatever. This is a gap easily jumped by 4.2V. Then the inductance keeps increasing the voltage as the gap increases in width until the arc can no longer be sustained.
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Sanding will eventually remove your plating. I recommend Scotch Brite Heavy Duty scrubber pads to bring down the high points that will just concentrate the current (and which have higher resistance) and encourage more arcing. Thereās nothing you can do about the pits but they donāt really affect anything and removing them means removing the plating and perhaps even more metal.
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When you clean it off and place ykur cells, give them couple spins so they are seated properly. Arcing is not the issue. The pressure is just too great for cells to be bouncing.
Also check if cell pvc is not caught between the contact and positive
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Will try, but you are right that the cells are held tight; itās hard to even spin them in place usually 
It cannot be simple oxidation as then that would be a problem for all NESE setups. What do you feel the issue is?
This is what can set up an arcing situation. It can keep the contacts from being tight together.
The cell bottoms can also flex from their concave resting state to convex under pressure/vibration. This can result in making/breaking contact in different spots even though the cell itself is firmly in place in one spot.
Just tossing out ideas for the arcing it appears to be for me. Looking forward to your theory on the cause.
Do you have a magnifier or loupe you can examine the contacts with after cleaning with alcohol (but before any sanding or scrubbing down of the high spots)? That would help a lot in determining what is happening here.
Iāll try to get some photos / figure out what it is this wekeend. I need the battery to commute tomorrow, lol. But my little brotherās 30Q NESE also has such marks, just not as large. I just assumed it was copper oxide, I guess.
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Pardon the diversionary question.
Do you (or anyone) have a loupe you like?
Iāve been thinking about getting a small, EDC magnifier to look at bugs and such with my toddler.
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A Bausch & Lomb Hastings Triplett is about as good as it gets IMHO, 5x and 10x will cover just about any need. But loupes are very hard for a lot of people to use (since they need to be positioned properly at the eye) and probably impossible for a toddler. They are tiny too.
I recommend a large handheld magnifier instead. Easy for kids to look through. I really like this one: https://www.amazon.com/gp/product/B088ZSFS17/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=
Oopsā¦you said small EDC type magnifier. Amazon will probably have some smaller ones too. 10x would probably be about right as the higher magnifications are smaller, have a limited depth of field, and are harder to āaimā.
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Ooooh good idea to pick one up for summer so we can burn some paper I mean learn about science
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I did this sometimes when I was a kid, great funā¦ But alsoā¦ Kind of cruel. 
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Most probable issue is trapped PVC. Happened to me couple times. Hard to see, thats why i always suggest spinning cells when seated. It is easy to detect if you have smart BMS. When charging, that group would jump ahead.
With simple BMS i would charge it some and then check the voltages on the groups. If one or couple stands out i would take a closer look.
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Itās definitely not trapped PVC, there are marks on literally every cell, every tab, in every module. Some more than others.
I donāt know why, but thereās a small dot pattern on a lot of those marks 
Alcohol isnāt really helping me clean them off 
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Those are, without a doubt, arcing marks. Iāve seen it hundreds of times with āmechanicalā vaping devices.
The alcohol will clean off some of the carbon and debris but the āburntā metal high points of the marks need to be removed because they just encourage more arcing. Scotch-Brite Heavy Duty pads can help some or emery cloth. The pits you cannot remove without taking off lots of metal.
The circular pattern is from the cells slowly rotating a little bit every time they bounce off the contact. As much as we might doubt that the cells are bouncing and moving the evidence is clear, these cells are not being held firmly in place.
Cells do not have a flat top or bottom contact and the NESE contacts are probably not flat either (convex most likely?). This results in just a few high points that are touching and when the contacts bounce this is where the arcing occurs.
The next time you use that setup place a mark on each cell when itās in the holder and see if the mark is in the same position after you take a ride. If not, then you have the proof that theyāre moving around.
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Yeah, that is arcing alright. Itās an issue in most mechanical electrical switches/relays because when they engage the contact always bounces. I donāt know whatās the state of the art solution for it, but some switches back in the day had mercury wetted contacts so the bounce happens while the surface is submerged in liquid metal.
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Sounds like something a small amount of copper foil (or any conductive metal foil) between the cell terminal and NESE contact would fix. Folded over itself a few times & shimmed in to conform to & bridge all high/low points.
Sounds like Winfly compression packs wouldnāt have this issue as it uses flexible braid instead of solid formed contacts
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It would be interesting to see that tested!
As long as the shims canāt move around much or abrade the insulation on the top of the cell.